1. Field of the Invention
The present invention relates to a plasma processing apparatus of the capacitive coupling type, used for performing a plasma process on a target substrate in, e.g. a semiconductor processing system. The term “semiconductor process” used herein includes various kinds of processes which are performed to manufacture a semiconductor device or a structure having wiring layers, electrodes, and the like to be connected to a semiconductor device, on a target substrate, such as a semiconductor wafer or a glass substrate used for an LCD (Liquid Crystal Display) or FPD (Flat Panel Display), by forming semiconductor layers, insulating layers, and conductive layers in predetermined patterns on the target substrate.
2. Description of the Related Art
For example, in manufacturing semiconductor devices, plasma processes, such as etching, sputtering, and CVD (Chemical Vapor Deposition), are often used for processing a target substrate or semiconductor wafer. There are various plasma processing apparatuses for performing such plasma processes, but parallel-plate plasma processing apparatuses of the capacitive coupling type are the ones in mainstream use.
In general, a parallel-plate plasma etching apparatus of the capacitive coupling type includes a process chamber with a pair of parallel-plate electrodes (upper and lower electrodes) disposed therein. When a process is performed, while a process gas is supplied into the chamber, an RF (radio frequency) power is applied to one of the electrodes to form an RF electric field between the electrodes, thereby causing RF electric discharge. The process gas is turned into plasma by the RF electric field, thereby performing, e.g. plasma etching on a predetermined layer disposed on a semiconductor wafer.
For example, there is an apparatus of this kind in which an RF power is applied to the lower electrode on which the semiconductor wafer is placed. In this case, the lower electrode serves as a cathode electrode, and the upper electrode serves as an anode electrode. The RF power applied to the lower electrode is used for plasma generation and also for an RF bias applied to the target substrate.
In the parallel-plate plasma processing apparatus of the capacitive coupling type, members present in the plasma generation region need to be protected from metal contamination and wear-out. For this reason, these members are made of quartz or formed of a body covered with a coating of an insulative ceramic with high resistance to plasma, such as Y2O3.
In recent years, design rules in manufacturing semiconductor devices have been increasingly miniaturized. Particularly, in plasma etching, it is required to improve the dimensional accuracy, selectivity relative to the mask and under-layer, and planar uniformity of the etching. For this reason, the recent trend is to use a lower pressure and lower ion energy in the process field within a chamber. This trend has brought about a use of an RF power with a frequency of 40 MHz or more, which is far higher than the frequency conventionally used.
However, where a lower pressure and lower ion energy are used, as described above, it becomes difficult to control the plasma uniformity because of increase in plasma resistivity. Specifically, where the frequency of an RF applied to an RF application electrode is set higher, when the RF is supplied from an RF power supply to the electrode backside, it is transmitted through the electrode surface by means of the skin effect and is concentrated at the central portion of the electrode main surface (surface facing the plasma). Consequently, the electric field intensity at the central portion of the electrode main surface becomes higher than the electric field intensity at the peripheral portion, so the density of generated plasma becomes higher at the electrode central portion than at the electrode peripheral portion. Thus the plasma resistivity becomes lower at the electrode central portion where the plasma density is higher, so an electric current is concentrated at the central portion of the counter electrode. As a result, the uniformity of the plasma density is further deteriorated, which brings about a poor planar uniformity and charge-up damage in plasma processing, such as etching
In order to solve this problem, a design is known in which the main surface central portion of an RF application electrode is formed of a high resistivity member (for example, Patent Document 1: Jpn. Pat. Appln. KOKAI Publication No. 2000-323456). According to this technique, the high resistivity member is employed for the main surface central portion of the RF application electrode to consume more RF power as Joule heat there. As a consequence, the electric field intensity on the main surface of the RF application electrode is more reduced at the electrode central portion than at the electrode peripheral portion, so that the poor uniformity described above in plasma density is remedied. However, the high resistivity member employed for the main surface central portion of an RF application electrode may consume too much RF power as Joule heat (energy loss), resulting in a low efficiency.